The present invention relates generally to ion implantation systems, and more particularly to an acceleration gap suitable for use in ion implantation systems.
Ion implantation systems are used to dope semiconductors with impurities in integrated circuit manufacturing. In such systems, an ion source ionizes a desired dopant element, which is extracted from the source in the form of an ion beam of desired energy. The ion beam is then directed at the surface of a semiconductor wafer in order to implant the wafer with the dopant element. The ions of the beam penetrate the surface of the wafer to form a region of desired conductivity, such as in the fabrication of transistor devices in the wafer. A typical ion implanter includes an ion source for generating the ion beam, a beamline assembly including a mass analysis apparatus for mass resolving the ion beam using magnetic fields, and a target chamber containing the semiconductor wafer or workpiece to be implanted by the ion beam.
In order to achieve a desired implantation for a given application, the dosage and energy of the implanted ions may be varied. The ion dosage controls the concentration of implanted ions for a given semiconductor material. Typically, high current implanters are used for high dose implants, while medium current implanters are used for lower dosage applications. The ion energy is used to control junction depth in semiconductor devices, where the energy levels of the beam ions determine the degree to which ions are implanted or the depth of the implanted ions. The continuing trend toward smaller and smaller semiconductor devices requires a mechanism which serves to deliver high beam currents at low energies. The high beam current provides the necessary dosage levels, while the low energy permits shallow implants.
In addition, the continuing trend toward higher device densities on a semiconductor wafer requires careful control over the uniformity of implantation beams being scanned across the workpiece. Another continuing trend is toward larger and larger semiconductor wafer sizes, such as 300 mm diameter wafers. Coupled with higher device densities, the larger wafer size increases the cost of individual wafers. As a result, control over implantation uniformity and other parameters is more critical than ever in avoiding or mitigating expenses associated with scrapping wafers.
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention is directed to an accelerator or accelerating structure and related methodology for accelerating/decelerating ions of an ion beam. The accelerator and related methodology are suitable for use in selectively implanting ions into a workpiece or wafer during semiconductor fabrication to selectively dope areas of the wafer. In addition to accelerating and/or decelerating ions, aspects of the present invention serve to focus as well as to deflect ions of an ion beam. This is accomplished by routing the ion beam through electrodes having potentials developed thereacross. The ion beam is also decontaminated as electrically neutral contaminants within the beam are not affected by the potentials and continue to travel generally along an original path of the ion beam. The electrodes are also arranged in such a fashion so as to minimize the distance the beam has to travel through the accelerator, thereby mitigating the propensity for beam blow up.
According to one aspect of the present invention, an accelerator suitable for use in implanting ions into a workpiece includes a first electrode having a first aperture formed therein and a second electrode having a second aperture formed therein. The first and second electrodes are oriented so as to be substantially parallel to one another, and the first and second apertures are aligned such that an axis substantially normal to the first and second electrodes passes through a gap defined between the first and second apertures and through coincident points in the first and second apertures. A potential developed between the first and second electrodes causes ions of an ion beam generally traveling along the axis to be accelerated or decelerated depending upon biasing of the potential as the ion beam passes into the first aperture and out through the second aperture. The accelerator also includes a first mid-gap electrode located between the first and second electrodes and above the gap, as well as a second mid-gap electrode located between the first and second electrodes and below the gap. A potential developed between the first and second mid-gap electrodes causes the ions within the ion beam to deflect away from the axis.
According to another aspect of the present invention, an accelerator suitable for use in implanting ions into a workpiece includes means for accelerating/decelerating ions of an ion beam and means for bending the ion beam by deflecting ions within the ion beam away from an axis along which the ion beam generally travels. The means for accelerating/decelerating and the means for bending operate independently of one another to accelerate/decelerate and bend the beam, respectively.
According to yet another aspect of the present invention, a method for accelerating/decelerating ions suitable for implanting ions into a workpiece includes developing a potential between a first pair of electrodes to accelerate/decelerate ions of an ion beam and developing a potential between a second pair of electrodes to deflect ions of the ion beam.
To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.